Milk flow profiles with an intermediate bimodality score are more efficient for milk harvesting

Milking is a labour intensive task on dairy farms. The milking duration of individual cows is a key factor determining herd milking times, with large variability existing between animals for a given milk yield. Examining milk flow profiles can aid understanding of this variability. Data on milking duration, milk yield, average and maximum milk flow rate, yield in the first 2 min, time to maximum milk flow rate, decline duration, bimodality score (defined as the proportion the milk flow rate decreased from the initial increase or peak in milk flow) and milk flow rate at predetermined intervals were collected daily from two farms in New Zealand between September 2011 and May 2012 to generate milk flow profiles. Residual milking duration (RMD) was calculated as the residual of milking duration regressed on milk yield. Milk flow profiles (n=63,534) were classified into four categories by bimodality score (0-0.25, 0.26-0.50, 0.51-0.75 and 0.76-1). Data were analysed with a linear mixed model that included the fixed effects of farm, parity, session, breed, days in milk, bimodality category and the random effect of cow. Average milk flow profiles for the four categories were derived from the least squares means of milk flow rate at each of the recorded time intervals. The optimum profile category by RMD had a bimodality score of 0.26-0.5 (mean 0.36). This category had the shortest time to maximum milk flow rate and greatest milk yield in the first 2 min. In this category the initial increase in milk flow rate was lower than in categories with a higher bimodality score, however, the milk flow rate did not subsequently decrease, and reached a significantly higher maximum milk flow rate than the 0-0.25 category. Differences in the shape of milk flow profiles may be related to cisternal volume or the proportion of milk yield in the cistern. Further studies are required to determine the relationship between physical udder traits and optimum milk flow profiles.